Narrowing of tubular cardiovascular structures such as heart valves may lead to non-physiological blood flows through the structures and consequently influence cardiovascular health of an individual. Valve calcification which is caused by calcium deposit, also known as plaque, on the valves may result in sclerosis (stiffening) of the tissue forming the valve leaflets and narrowing of the valve opening. This narrowing can progress to become severe enough to reduce blood flow through the aortic valve and to increase strain on the left ventricle, causing a valve stenosis (i.e. valve narrowing). The aortic valve is one of the heart valves with high prevalence of stenosis. The aortic valve stenosis is the second most common cardiovascular disease, having an incidence rate of 2-7% in the Western European and North American populations aged beyond 65 years. Ultimately, aortic valve stenosis may lead to symptoms including shortness of breath, chest discomforts and fainting. Left untreated, severe aortic stenosis can lead to death in up to 50 percent of patients.
Management of patients with aortic stenosis typically depends on the severity of the disease. When the aortic stenosis becomes severe, aortic valve replacement might be necessary. Transcatheter aortic valve implantation (TAVI) is the replacement of the aortic valve of the heart by a stent-based valve mounted on a catheter inserted into the body via a small incision, as opposed to valve replacement by open heart surgery. The TAVI procedure involves accessing a femoral artery, performing balloon valvuloplasty, then advancing an artificial aortic valve across the native valve using a catheter. During rapid right ventricular pacing, a balloon is inflated to deploy the artificial valve. Strokes can be a major complication during TAVI procedures. Embolization risk due to plaque rupture and paravalvular leakages, in which blood flows through a channel between the structure of the implanted valve and the cardiac tissue due to a lack of appropriate sealing, are drawbacks of TAVI interventions. Calcification assessment can be used for assessing the suitability of a patient for TAVI procedure, as well as for risk assessment, positioning of an aortic valve implant, and selection of a type of aortic valve implant.
In the assessment of calcifications, apart from the amount of calcification also its distribution is important. It has been shown that the distribution of the plaque load over the three aortic valve leaflets, also known as valve cusps (left coronary cusp (LCC), right coronary cusp (RCC), and non-coronary cusp (NCC)), is often asymmetric. The unequal distribution of calcifications is one risk factor for paravalvulvar leakage.
It is known to automatically evaluate aortic valve calcification. For example, in US 2013/155064 a method and system for automatic aortic valve calcification evaluation is described. According to US 2013/155064 a patient-specific aortic valve model in a 3D medical image volume, such as a 3D computed tomography (CT) volume is provided. Calcifications in a region of the 3D medical image volume are defined based on the aortic valve model. A 2D calcification plot is generated that shows locations of the segmented calcifications relative to aortic valve leaflets of the patient-specific aortic valve model. It is said that the 2D calcification plot can be used for assessing the suitability of a patient for a Transcatheter Aortic Valve Replacement (TAVI) procedure, as well as risk assessment, positioning of an aortic valve implant, and selection of a type of aortic valve implant. A problem of the method of US 2013/155064 is that it is insufficiently accurate for the assessment of aortic valve calcifications.